Negative Magnetoresistance Effect Research Articles

Effect of negative magnetoresistance in a transverse magnetic field in quantum Bi wires

We observed for the first time the effect of the negative magnetoresistance (NMR) in transverse magnetic fields (B ⊥ I) in quantum Bi wires at 4.2 K; this effect is described in this work. The single crystal bismuth wires in a glass cover were produced using the liquid phase casting methods. The Bi wires are strictly cylindrical with the (1011) orientation along the wire axis and diameters ranging from 50 to 400 nm. In wires with a diameter of d < 80 nm, there was observed a semimetal-semiconductor transition, which is associated with the quantum size effect and is attended with a “semiconductor” temperature dependence of the resistance R(T). In weak transverse magnetic fields, there was observed an NMR effect both at B ‖ C2 and at B ‖ C3. The increase in the wire diameter d, temperature T, and magnetic field B results in the weakening and total disappearance of the found peculiarities of NMR in weak magnetic fields, thus reflecting the suppression of the size quantization effect. An analytical simulation of the quantum wire that makes it possible to explain the nonmonotonic character of the transverse magnetoresistance in Bi wires is considered. To interpret this NMR effect, we have used a theoretical model in which the electrical conductivity is calculated using the Cubo formula with account for the elastic scattering of the carriers on phonons and the size quantization of the energy spectrum. The comparison of the experimental results with the analytic model allows us to conclude that the observed NMR effect in the transverse magnetic field in Bi nanowires has a quantum nature.

Phase diagram of the ZnSnAs2–MnAs system

Six equilibrium samples of (1−x)ZnSnAs2+xMnAs (x=0, 0.1, … 0.5mol.%) and one quenched sample of 0.8ZnSnAs2+0.2MnAs were synthesized. The samples were studied with X-ray, DTA, MFM and SEM. The system ZnSnAs2–MnAs has eutectic point with coordinates 45±2mol.% MnAs and 744±10°C. The eutectic compound contains isolated, practically round shape inclusions of MnAs in the host ZnSnAs2. Based on the earlier investigations, we predict negative magnetoresistance effect in this semiconductor–ferromagnet compound with nanogranular structures. The lattice parameters of ZnSnAs2 without manganese arsenide and ZnSnAs2+MnAs are similar, meaning MnAs does not influence the lattice parameters. Therefore one can make conclusion that solubility of the MnAs in ZnSnAs2 is low. The lattice parameters are a=5.8509Å, c=11.7135Å for tetragonal and a=5.8558Å for cubic symmetry. The density of the ZnSnAs2 calculated from the HR-XRD is 5.5314g/cm3 for tetragonal and 5.5230g/cm3 for cubic structure.

Nonlinear transport in two-dimensional electron gas exhibiting colossal negative magnetoresistance

We report on nonlinear transport measurements in a GaAs/AlGaAs quantum well exhibiting a colossal negative magnetoresistance effect. Under applied dc bias, the magnetoresistance becomes nonmonotonic, exhibiting distinct extrema that move to higher magnetic fields with increasing current. In the range of magnetic fields corresponding to the resistivity minimum at zero bias, the resistivity increases linearly with current and the rate of this increase scales with the inverse magnetic field. The latter observation is consistent with the theory, proposed more than 35 years ago, considering classical memory effects in the presence of strong, dilute scatterers.

Preparation and Properties of Ferromagnetic Antiperovskite Co&lt;sub&gt;3&lt;/sub&gt;FeN Thin Films

Thin films of Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> FeN with an antiperovskite structure were epitaxially grown on (La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.18</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.82</sub> )(Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.59</sub> Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.41</sub> )O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (001) substrates by reactive magnetron sputtering. The influence of the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> volume concentration in the sputtering gas mixture on the structure and properties of Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> FeN thin films was systematically investigated. The optimized Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> FeN thin films exhibited a saturation magnetization, Ms, of 1350 emu/cc, which is comparable with the theoretical value. A negative anisotropic magnetoresistance (AMR) effect with an AMR ratio of up to -0.88% was observed at 4.2 K.

Large negative magnetoresistance induced by anionic solid solutions in two-dimensional spin-frustrated transition metal chalcogenides.

We report an anionic solid solution process that induces frustrated magnetic structures within two-dimensional transition metal chalcogenides, which leads to huge negative magnetoresistance effects. Ultrathin nanosheets of TiTe(2-x)I(x) solid solutions, which are a new class of inorganic two-dimensional magnetic material, exhibit negative magnetoresistance with a value of up to -85%, due to the spin-dependent scattering effects of local Ti(3+) 3d(1) moments that are antiferromagnetically coupled. Moreover, TiTe(2-x)I(x) serials show unique transport behaviors with continuous evolution from metallic to semiconducting states. We anticipate that anionic doping will be a powerful tool for optimizing the intrinsic physical properties of two-dimensional transition metal chalcogenide system.

The Positive and Negative Magnetodielectric Effects in Double Perovskite Pr2CoMnO6

The magnetic, electric, and dielectric properties of a B‐site ordered double perovskite Pr2CoMnO6 were investigated. A charge localization state and a negative magnetoresistance effect were observed below 250 K. Different from other double perovskites, one negative and two positive magnetodielectric effects were simultaneously observed in this sample. The physical origins of these interesting magnetodielectric properties were discussed.

Construction of a soft X-ray diffractometer with a 7.5-T superconducting magnet

We have constructed a soft X-ray diffractometer with a 7.5-T superconducting magnet in order to study ordered electronic structures under high magnetic field. In this paper, we present the features of this system and an example of resonant soft X-ray scattering measurement under the magnetic field of (LaMnO3)3(SrMnO3)3 superlattice with a remarkable negative magnetoresistance effect.

Giant Current-Perpendicular-to-Plane Magnetoresistance in Multilayer Graphene as Grown on Nickel

Strong magnetoresistance effects are often observed in ferromagnet-nonmagnet multilayers, which are exploited in state-of-the-art magnetic field sensing and data storage technologies. In this work we report a novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as grown on a catalytic nickel surface by chemical vapor deposition. A negative magnetoresistance effect of ∼10(4)% has been observed, which persists even at room temperature. This effect is correlated with the shape of the 2D peak as well as with the occurrence of D peak in the Raman spectrum of the as-grown multilayer graphene. The observed magnetoresistance is extremely high as compared to other known materials systems for similar temperature and field range and can be qualitatively explained within the framework of "interlayer magnetoresistance" (ILMR).

The spin-filter capability and giant magnetoresistance effect in vanadium–naphthalene sandwich cluster

Using density functional theory and non-equilibrium Green’s function technique, we performed theoretical investigations on the magnetic and transport properties of V2n(C10H8)n+1 (n=1–4) sandwich clusters. For the ground states, our results show that all the clusters are stable and possess ferromagnetic orders. The smaller clusters have higher stabilities, and our predictions are in agreement with the experimental observation. The double exchange mechanism plays an important role in determining the magnetic properties of the systems. Furthermore, with Ni as electrodes, the clusters exhibit interesting transport properties such as significant spin-filter capability, negative differential resistance feature and giant magnetoresistance effect. These findings suggest that V2n(C10H8)n+1 sandwiches are excellent candidates for application in spintronics and organic electronics.

Effect of a Highly Metallic Surface State on the Magneto-Transport Properties of Single Crystal Bi Films

The magneto-transport properties of thin single crystal Bi films epitaxial grown on Si (111)-7 × 7 surfaces are investigated systematically as functions of film thickness (5–55 nm) and temperature. Under a perpendicular magnetic field, the positive magnetoresistance (PMR) effect is normally found, and its curve shapes are evolved systematically with film thickness. In contrast, under parallel magnetic fields the PMR effect observed for thinner Bi films develops into the negative magnetoresistance effect with the increasing magnetic field for the thicker Bi film. Our analysis indicates that there exists strong competition between the weak anti-localization effect in the surface states and the weak-localization effect in the bulk states of the Bi film, which induces the anomalous changes in the parallel magneto-resistance curves. The temperature-dependent experiments further demonstrate that the surface state plays an important role in the magneto-transport process of Bi films.

Vortex-induced negative magnetoresistance and peak effect in narrow superconducting films

In the framework of the Ginzburg-Landau model, it is shown that narrow superconducting films with width $w\ensuremath{\simeq}3--8\ensuremath{\xi}(T)$ [$\ensuremath{\xi}(T)$ is a temperature-dependent coherence length] exhibit unusual transport properties. In the absence of bulk pinning, its critical current ${I}_{c}$ nonmonotonically depends on perpendicular magnetic field $H$ and has one minima (dip) and one maxima (peak) at some magnetic fields. At currents $I\ensuremath{\ll}{I}_{c}(H)$, the finite magnetoresistance $R(H)$ of such a sample due to thermoactivated vortex hopping via edge barriers also shows both local maxima (peak) and minima (dip) nearly at the same magnetic fields. In narrower films, such an effect is absent due to absence of the vortices and in wider films the effect is weaker due to increased vortex-vortex interaction. The finite length of the film produces additional periodic variation in both ${I}_{c}(H)$ and $R(H)$ because of discrete changes in the number of the vortices, which is superimposed on the above-mentioned nonmonotonic dependence. The obtained results are directly related to many experiments on narrow superconducting films/bridges where such nonmonotonic dependencies ${I}_{c}(H)$ and $R(H)$ were observed.

Study of the transport properties of La0.8Ba0.2MnO3/SrTiO3:Nd heterojunctions under reverse bias

Heterojunctions composed of P-type La0.8Ba0.2MnO3 and N-type Nd doped SrTiO3 are successfully fabricated via chemical solution deposition. Good rectifying property is obtained. Detailed studies of the transport properties under reverse bias show that above the metal-insulator transition temperature TMI, the Frenkel–Poole emission dominates the leakage current and the emission barrier height was extracted. When placed in magnetic field, the junctions show different transport behaviors below and above TMI. It shows negative magnetoresistive effect below TMI and positive one above TMI. This is explained by the phase separation mechanism and the band structure of manganites.

Electrical properties of thermoelectric cobalt Ca3Co4O9 epitaxial heterostructures

Heterostructures fabricated from layered cobalt oxides offer substantial advantages for thermoelectric applications. C-axis-oriented Ca3Co4O9 (CCO) thin films on SrTiO3 substrates and Ca3Co4O9/SrTi0.993Nb0.007O3 p-n heterojunctions were fabricated by pulsed laser deposition. The measurements of in-plane resistivity, thermopower, and magnetic properties performed on the Ca3Co4O9 thin films were found to be comparable to ab-plane those of the single crystals due to good orientation of the films. The temperature dependence of the electrical transport properties of Ca3Co4O9/SrTi0.993Nb0.007O3 p-n heterojunction was also investigated. The junction shows two distinctive transport mechanisms at different temperature regimes under forward bias: tunneling across the Schottky barrier in the temperature range of 100-380 K, and tunneling mechanism at low bias and thermal emission mechanism at high bias between 10 and 100 K. However, for the case of low reverse bias, the trap assisted tunneling process should be considered for the leakage current. Negative magnetoresistance effect is observed at low temperatures, related to the electron spin-dependent scattering and the interface resistance of the heterostructures.

Giant Magnetoresistance Effect in the Metal–Insulator Transition of Pyrochlore Oxide Nd2Ir2O7

We investigated the magnetoresistance (MR) effect of the pyrochlore oxide Nd2Ir2O7, which shows a metal-insulator transition at T_MI =33 K. A small positive MR effect was observed in the metallic state above T_MI, while a large negative MR effect was observed in the insulating state below T_MI . MR effects exceeding 3000% were found at 1 K at a field of 9 T. As a result, we confirmed the crossover from the insulating state to a state with a small or partial band gap in a field up to 56 T. Furthermore, from the MR effect in Eu2Ir2O7 (T_MI = 120 K) and Gd$_2$Ir$_2$O$_7$ (T_MI = 127 K), we revealed that the large negative MR effect of the pyrochlore iridate Ln2Ir2O7 depends on the magnetism of the lanthanide Ln^{3+} ion. The d-f interaction plays a significant role in the large negative MR effect in the insulating state.

Negative magnetoresistance and anomalous Hall effect in GeMnTe-SnMnTe spin-glass-like system

Magnetotransport properties of spin-glass-like Ge1−x−ySnxMnyTe mixed crystals with chemical composition changing in the range of 0.083≤x≤0.142 and 0.012≤y≤0.119 are presented. The observed negative magnetoresistance we attribute to two mechanisms, i.e., weak localization occurring at low fields and spin disorder scattering giving contribution mainly at higher magnetic fields. A pronounced hysteretic anomalous Hall effect (AHE) was observed. The estimated AHE coefficient shows a small temperature dependence and is dependent on Mn-content, with changes in the range of 10−7&amp;lt;RS&amp;lt;10−6m3/C. The scaling law analysis has proven that the AHE in this system is due to the extrinsic mechanisms, mainly due to the skew scattering accompanied with the side jump processes.

Metal–insulator–metal transition in Ti substituted antiferromagentic Ru2MnGe Heusler alloy

We report the composition-induced metal–insulator crossover transition in Ti substituted Ru-based metallic full Heusler alloy Ru2MnGe where the both end of materials shows a metallic properties. The samples at the middle composition show the large negative magnetoresistance effect. The experimental results of the resistivity and the magnetization indicate that this metal–insulator transition is induced by the Kondo effect because Ti atoms on antiferromagnetic Ru2MnGe have an important role in appearance of insulator states.

The quantum phase slip phenomenon in superconducting nanowires with a low-Ohmic environment

In a number of recent experiments it has been demonstrated that in ultra-narrow superconducting channels quantum fluctuations of the order parameter, alternatively called quantum phase slips, are responsible for the finite resistance well below the critical temperature. Acceptable agreement between those experiments and the models describing quantum fluctuations in quasi-one-dimensional superconductors has been established. However, the very concept of phase slip is justified when these fluctuations are relatively rare events, meaning that the effective resistance of the system should be much smaller than the normal state equivalent. In this paper we study the limit of the strong quantum fluctuations where the existing models are not applicable. In the particular case of ultra-thin titanium nanowires, it is demonstrated that below the expected critical temperature the resistance does not demonstrate any trend towards the conventional for a superconductor zero-resistivity state even at negligibly small measuring currents. The application of a small magnetic field leads to an unusual negative magnetoresistance, which becomes more pronounced at lower temperatures. The origin of the negative magnetoresistance effect is not clear.

Observation and study of the negative magnetoresistance in porous silicon

We investigate the effect of a static magnetic field on the electrical properties of thin films of porous silicon. We observe a relative variation of the resistance with respect to intensity of the applied magnetic field. This effect called magnetoresistance (MR) has been found to be negative at room temperature in the entire range of the applied magnetic field (under 8000G). The negative MR effect depends strongly of the applied voltage and reaches up to 5% at the value of magnetic field of 8000G. The analysis has been based on the 1D weak localization theory (WL) in diffusive semiconductors, from which a consistent picture emerges, considering the PS film as networks of quasi-one-dimensional wires. We give an explicit expression for the WL correction depending only of the phase coherence length Lφ. A good agreement is observed between experimental data and theory.

Negative giant magnetoresistance effect in single layered superparamagnetic polymer nanocomposite structures of poly(vinyl alcohol)–polyaniline/bismuth ferrite

Superparamagnetic polyaniline/bismuth ferrite (PANI/BFO) nanocomposite powder is synthesized through an in situ sol–gel polymerization method and it is embedded in non-magnetic poly(vinyl alcohol) (PVA) matrix to fabricate high performance flexible films. The interaction between PANI/BFO filler and PVA matrix and hence the formation of composite is identified through XRD and it is further confirmed through FTIR spectra. Vibration sample magnetometry (VSM) studies ensure the superparamagnetic nature of the composite films. The magnetoresistance measurements are made at room temperature for various current values from which it is observed that the samples exhibit a negative giant magnetoresistance (GMR) effect. The variation of GMR from 21% to 66% with filler concentration and also the non-ohmic V–I characteristics of the composite films are reported.

Negative Anisotropic Magnetoresistance in γ'-Fe4N Epitaxial Films on SrTiO3(001) Grown by Molecular Beam Epitaxy

We observed the negative anisotropic magnetoresistance (AMR) effect in γ'-Fe4N epitaxial films grown on SrTiO3(001) substrates using molecular beam epitaxy. The AMR ratio was increased immediately below 50 K. The angular dependence of AMR ratio contained not only cos 2θ but also cos 4θ components, and the sign of Fourier coefficient of cos 4θ term was changed around 10 K. These behaviors are in good agreement with those already reported for γ'-Fe4N pseudo-single-crystal films on MgO(001) substrates formed by sputtering. These behaviors might be attributed to temperature dependence of electronic or magnetic structure specific to γ'-Fe4N.